Is it possible to control a value in all of my materials with one click?
How to tweak values inside any material with a driver in the current scene's properties :
Step by Step :
Go into the Scene properties, expand the Custom Properties foldout and click on Add to add a new custom property.
Right click in the field, choose Copy as New Driver
Then right click into the field you want to be driven by the custom property, and choose Paste Driver
Now the purple fields get updated when you change the custom property in the Scene properties.

Notes :

You neeed blender 2.81 + to have access to the &quot;Copy as new driver&quot; context choice
Notice the purple tint in the driven fields. That means you can't change directly the values anymore. If you want to get rid of the driver, right click in the field then choose &quot;Delete Driver&quot;